1. Field
A linear compressor and a method for controlling a linear compressor are disclosed herein.
2. Background
In general, a compressor is an apparatus that converts mechanical energy into compression energy of a compressible fluid, and constitutes a part of a refrigerating device, for example, a refrigerator, or an air conditioner. Compressors are roughly classified into a reciprocating compressor, a rotary compressor, and a scroll compressor. The reciprocating compressor is configured such that a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between a piston and a cylinder and the refrigerant is compressed as the linearly reciprocates in the cylinder. The rotary compressor is configured such that a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an eccentrically-rotatable roller and a cylinder and the refrigerant is compressed as the roller eccentrically rotates along an inner wall of the cylinder. The scroll compressor is configured such that a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an orbiting scroll and a fixed scroll and the refrigerant is compressed as the orbiting scroll rotates along the fixed scroll.
The reciprocating compressor sucks, compresses, and discharges a refrigerant by linearly reciprocating the piston within the cylinder. The reciprocating compressor is classified into a recipro type and a linear type according to a method of driving the piston.
The recipro type refers to a type of reciprocating compressor that converts a rotary motion of a motor into a linear reciprocating motion by coupling the motor to a crankshaft and coupling a piston to the crankshaft. On the other hand, the linear type refers to a type of reciprocating compressor that reciprocates a piston using a linear motion of a linearly-moving motor by connecting the piston to a mover of the motor.
The reciprocating compressor includes a motor unit or device that generates a driving force, and a compression unit or device that compresses fluid by receiving the driving force from the motor unit. A motor is generally used as the motor unit, and specifically, the linear type reciprocating compressor uses a linear motor.
The linear motor directly generates a linear driving force, and thus, does not require a mechanical conversion device and a complicated structure. Also, the linear motor may reduce a loss due to energy conversion, and remarkably reduce noise by virtue of the non-existence of a connection portion at which friction and abrasion are caused. Also, when the linear type reciprocating compressor (hereinafter, referred to as a “linear compressor”) is applied to a refrigerator or air conditioner, a compression ratio may vary by changing a stroke voltage applied to the linear compressor. Accordingly, the compressor may also be used for a control of varying a freezing capacity.
In the linear compressor, as the piston is reciprocated without being mechanically locked within the cylinder, the piston may collide with (or crash into) a wall of the cylinder when an excessive voltage is applied suddenly, or a compression may not be properly executed when the piston fails to move forward due to a great load. Therefore, a control device for controlling the motion of the piston in response to a variation of the load or voltage is needed.
In general, a compressor control device executes a feedback control by detecting voltage and current applied to a compressor motor and estimating a stroke in a sensor-less manner. In this instance, the compressor control device includes a triac or an inverter that controls the compressor.
The linear compressor performing the feedback control can detect a top dead center (TDC) of the piston only after the piston collides with a discharge valve provided on a discharge unit or device of the cylinder, thereby generating noise due to the collision between the piston and the discharge valve. That is, when the piston collides with the discharge valve in the general linear compressor, a stroke estimation is executed to determine that the piston reaches the TDC of the cylinder. Accordingly, collision noise between the piston and the discharge valve is inevitable.